The 23 other passengers and crew were rescued on Sunday, pulled from the water by local fishermen and search and rescue teams. The survivors spent more than 36 hours in the water.

The two missing people are believed to be Spanish, other passengers on board said -- though officials at the Spanish foreign ministry could not confirm this.

The tourists -- mostly from Europe -- were on what was supposed to be an exotic getaway: a cruise from west to east, departing from the island of Lombok -- which lies opposite Bali -- in the province of West Nusa Tenggara and ending in Labuan Bajo, in East Nusa Tenggara, with a number of stops along the way. Under normal conditions, the journey would take four nights to complete.

Boat hits rocks

Everything appeared fine when the vessel, named Versace Amara, set sail last Thursday. Three days into the trip, the boat ran into trouble.

Budiawan, head of the rescue mission, who like many Indonesians goes by one name, says it's believed the boat hit rocks off Sangeang, at about 1 a.m. local time on Saturday morning. Water began leaking into the vessel, forcing the passengers and crew to abandon ship. The vessel was carrying 20 tourists, three crew and two local guides.

Budiawan said authorities were first notified of the incident on Sunday morning and immediately deployed rescuers to the site. The nearest town is Bima on the island of Sumbawa -- a two-hour boat ride away from where the boat sank.

Recounting the disaster, one of the survivors said the group decided to split into two. "There was a coastline visible, a deserted island about five kilometers (3.1 miles) through rough water," Tony Lawton from New Zealand told CNN affiliate the Seven Network.

The 10 strongest swimmers decided to swim for the coast and they thought they'd probably survive it and luckily they did, but it was very close.Survivor

"The 10 strongest swimmers decided to swim for the coast and they thought they'd probably survive it and luckily they did, but it was very close."

In the end, Lawton said the group got within half a kilometer of shore but were exhausted. They were able to wave at a group of fishermen on the beach, who went out to retrieve half of them on Sunday afternoon.

Search officials say the other five were picked up by rescue crews. All from the first group were taken to hospital in Bima.

Another 13 passengers and crew stayed in the water near the sunken boat, using lifebuoys and life vests to stay afloat. They were retrieved by local fishermen on Sunday evening, in the waters of Sape. They've since been treated in hospital, and eight are staying at a hotel in Bima, waiting for officials from their respective consulates to arrive to help them.

Lack of equipment

Another survivor, Spanish national Rafael Martinez, criticized the lack of equipment on the boat. "There was no security, no radio, no GPS, no navigation equipment. There were nothing," he told CNN affiliate Trans7 Indonesia.

"Only life jacket, but life jacket, it doesn't work. If you're in the middle of the ocean with a life jacket, what happens? Nothing."

"This problem should have been solved very, very easy," another unidentified survivor told the Seven Network. "We could have had a boat coming to rescue us in one hour, if they would have had any machine, radio, GPS or anything that all the boats will have. But without everything, maybe people are dead."

However, the tour operator rejected the survivors' claims. Tajudin Sam, owner of Eriksa Travel Agency, told CNN there was equipment on board to call for help. "I admit no GPS, but the boat had two radio communications and was working well," he said.

Tajudin said the boat was only three months' old and modeled on a traditional Phinisi sail boat -- but with a motor. He did admit he did not have a full list of the passengers' names and passport numbers.

"We normally do not make copies of the passports of the tourists for the cruise," he said. "Passengers usually write down their own names and passport numbers on a list -- that's why in this case, some tourists wrote only their first names. I cannot read some of their handwriting clearly."

The two tourists still missing are believed to be male adults.

Budiawan said it's believed the missing men, who were with the second group, became separated owing to strong currents.